The present invention relates to a method for appropriate evaluation of skin conditioning-ameliorating agents for improving unfavorable skin conditions such as wrinkles or chapped skin or preventing skin conditions from getting worse and compositions for topical application to skin for use in ameliorating skin conditions (hereinafter sometimes simply referred to as xe2x80x9ccomposition for topical application to skinxe2x80x9d) containing the above agents and to a method of producing compositions for topical application to skin having a sufficient skin conditioning-ameliorating effect.
Though everybody cannot stop seeking beautiful and clear skins, skin conditions change due to various factors. For example, formation of wrinkles varies depending on age, taking care of the skin or damages caused by light or the like. At present, there is no. established theory for such basic questions as xe2x80x9cwhat wrinkles arexe2x80x9d or xe2x80x9cwhy wrinkles formxe2x80x9d. Further, there are various theories such that xe2x80x9cwrinkles are caused by the change of the structure of elastinxe2x80x9d or that xe2x80x9cwrinkles are attributed to decrease of the amount of collagenxe2x80x9d. However, phenomenon contrary to these theories are sometimes observed. Thus, changes of skin conditions represented by formation of wrinkles have not been elucidated completely without contradiction.
On the other hand, a number of skin conditioning-ameliorating agents and compositions for topical application to skin containing such agents have been developed so far to ameliorate unfavorable skin conditions such as wrinkles as described above or to prevent worsening of such skin conditions. Evaluation of such agents had to largely depend on the method of functionally evaluating changes of the skin surface on which the above skin conditioning-ameliorating agent is applied. In other words, there was no universal evaluation standard to screen, from various drugs and preparations, those enabling amelioration of the skin conditions or prevention of their worsening as described above, and therefore, appropriate evaluation could not be given to skin conditioning-ameliorating agents and compositions for topical application to skin containing such agents.
Thus, in order to seek methods for ameliorating skin conditions or preventing skin conditions from getting worse, it is very important to identify changes of skin conditions correctly, particularly quantitatively. Nevertheless, such identification methods have not been obtained so far. Thus, it has been desired to develop methods for identifying changes of skin conditions correctly for appropriate evaluation of skin conditioning-ameliorating agents and the like.
Under these circumstances, the present invention was made. An object of the present invention is to provide a method for appropriately evaluating a skin conditioning-ameliorating agent for improving unfavorable skin conditions or preventing skin conditions from getting worse and a composition for topical application to skin containing the above agent for use in ameliorating skin conditions. Another object of the present invention is to provide a method of producing a composition for topical application to skin containing the skin conditioning-ameliorating agent, which has a sufficient skin conditioning-ameliorating effect.
The term xe2x80x9cskin conditioning-ameliorating agentsxe2x80x9d used herein means drugs consisting of only effective components for amelioration of skin conditions having a skin conditioning-ameliorating effect or an effect to prevent worsening of skin conditions.
In order to achieve the above objects, the present inventors sought means of appropriately identifying changes of skin conditions such as wrinkles by conscientiously observing tissues in the course of actual formation of wrinkles. As a result of intensive investigations, it was found that the structure of collagen fiber bundle in dermis was in disorder and is unclear when the skin conditions were unfavorable such as wrinkles or chapped skin. In other words, it was found that skin conditions and their changes such as wrinkle formation or amelioration of wrinkles could be identified by using the degree of order of collagen fiber bundle in dermis as an index, thereby completing the present invention. It has not been known at all so far that skin surface morphology and dermis morphology correlate well to each other, particularly that a groove corresponding to a wrinkle on the skin surface is formed as well as on dermis.
Thus, the present invention provides a method for evaluating a skin conditioning-ameliorating agent or a composition for topical application to skin containing the agents using an animal having at least one skin portion with bad conditions, which comprises the steps of applying to the skin portion the skin conditioning-ameliorating agent or the composition for topical application to skin containing the agent and evaluating the agent or the composition using as index changes of the degree of order of dermis collagen fiber bundle at the skin portion before and after application of the agent or the composition.
According to the evaluation method of the present invention, a skin conditioning-ameliorating agent or a composition for topical application to skin containing the agent that can greatly ameliorate the degree of order of dermis collagen fiber bundle is considered to be excellent in a skin conditioning-ameliorating effect.
Animals for use in the method for evaluation of the present invention have at least one skin portion with bad conditions. Specifically, the bad conditions of skin include wrinkles, chapped skin, and the like.
The animals having at least one skin portion with bad conditions used in the present invention specifically include mice which have been exposed to irradiation of ultraviolet light for a long time, guinea pigs whose skin on the back has been shaven and coated with an anionic surface active agent, and the like.
According to the method for evaluation of the present invention, the degree of order of dermis collagen fiber bundle can be determined by taking microphotographs of a specimen of dermis, which has been prepared by excising at least a part of the above-described skin portion, at magnifications of 100 to 10,000 and judging the microphotographs based on the following criterion.
[Criterion for judging]
0: No collagen fiber bundle structure is observed in all observation area.
1: Disintegration or conversion to abnormal structure of collagen fiber bundle structure is observed in more than half of the observation area.
2: Disintegration or denaturation of collagen fiber bundle structure is observed in part, but almost normal structure is retained as a whole.
3: Normal collagen fiber bundle structure is observed over the whole area with almost no disintegration and denaturation.
When the above criterion for judging is used for the degree of order of collagen fiber bundle of dermis in the evaluation method of the present invention, skin conditioning-ameliorating agents and the like that are given better scores after their application than those before their application are considered to be excellent in a skin conditioning-ameliorating effect.
The present invention also relates to a method of producing a composition for topical application to skin containing a skin conditioning-ameliorating agent and provides a method of producing a composition for topical application to skin which comprises the steps of providing an animal having at least one skin portion with bad conditions, applying to the skin portion the composition for topical application to skin once per day for consecutive 8 weeks in an amount of 0.01 g/10 cm2/one application, taking microphotographs of a specimen of dermis prepared by excising at least a part of the skin portion, at magnifications of 100 to 10,000, judging the microphotographs based on the above-described criterion for judging to determine the degree of order of dermis collagen fiber bundle of the part of the skin portion before and after application of the composition, and adjusting the content of the skin conditioning-ameliorating agent so that the value calculated by dividing the degree of order of dermis collagen fiber bundle after application of the composition by that before application should be not less than 1.5.
Specifically, the composition for topical application to skin to which the above method of the present invention can be applied includes wrinkle-ameliorating cosmetics, chapped skin-ameliorating cosmetics, and the like.